This invention relates to alpha numeric displays and more particularly to a monolithic light emitting diode display. More particularly, the invention is related to a light emitting diode display which is scannably addressable.
Visual readout devices such as alpha numeric displays are available in several formats utilizing various light emitting devices such as incandescent lamps, gaseous discharge lamps, electroluminescent arrays and more recently, light emitting diode arrays. Such devices are utilized for many purposes such as computer readouts, process control instrumentation, aircraft and automotive instrument panels, and various other indicators such as clocks and gauges. Since most, if not all of the aforementioned uses, rely on semiconductor electronics, it is highly desirable that the alpha numeric display be compatible with the voltages and currents normally utilized in such semiconductor circuits and be compatible with its speed of operation. The major objection to the presently most widely used visual readout, the gas discharge lamp of the cathode glow variety, is the high voltage required for initiating the glow discharge. Such readouts require the use of interface semiconductors having high reverse voltage breakdown characteristics. Obviously, the light emitting diode array format, being itself a semiconductor device, is highly desirable for a visual readout since it is inherently compatible with the electronics of the semiconductor circuits.
Some attempts have been made to provide alpha numeric displays utilizing light emitting diodes in either discrete, hybrid or individually addressable diode bit arrays. In these formats, light emitting diode arrays have not been widely acceptable, as they are costly, unreliable and relatively inconvenient to adapt to standard systems.